Reaction motor fuel



y 1961 J. M. BURTON ET AL 2,993,335

REACTION MOTOR FUEL Filed Sept. 15, 1956 8 INVENTORS J. M. BURTON H. M.FOX BY flan/WW ATTORNEYS .LlI-IHNEHHVd $338930 233,335 Patented July 25,1961 ice 2,993,335 REACTION MOTOR FUEL Joe M. Burton, Waco, Tex., andHomer M. Fox, Bartlesville, kla.,'assignors to Phillips PetroleumCompany, a corporation of Delaware Filed Sept. 1'3, 1956, Ser. No.609,774

'19 Claims. (Cl. 6035.4)

This invention relates to reaction motor fuels. In one aspect thisinvention relates to rocket propellants. In another aspect thisinvention relates to hypergolic fuel. In another aspect, this inventionrelates to the application of hypergolic fuels to the propulsion ofrockets. In another aspect this invention relates to fast-burning fuels.

This application is a continuation-in-part of our co pendingapplication, Serial No. 400,441, filed December 28, 1953, now abandoned.

Our invention is concerned with new and novel reaction motor fuels andtheir utilization. A rocket, or jet propulsion device, is defined hereinas a rigid container for matter and energy, so arranged that a portionof the matter can absorb energy in kinetic form and subsequently beejected in a specified direction. One type of reaction motor to whichour invention is applied is that type of .jet propulsion devicedesignated as a pure rocket, i.e., a thrust producer which does not makeuse of the surrounding atmosphere. A rocket of this type is propelled byintroduction of a propellant material into a combustion chamber therein,and burning it under conditions that will cause it to release energy ata high but controllable rate immediately after entering into thecombustion chamber. Rocket propellants, as liquids, are advantageouslyutilized, inasmuch as the liquid propellant material can be carried in alight-weight, low-pressure vessel and pumped into the combustionchamber, the latter, though it must withstand high pressure andtemperature, being only necessarily large enough to insure combustion.Also, the flow of liquid propellant into the combustion chamber can beregulated at will so that the thrust, continuous or an intermittentburst of power, can be sustained. The latter type of liquid propellantflow contributes to a longer life of the com-bustion chamber and thrustnozzle.

Various liquids and liquid combinations have been found useful as rocketpropellants. Some propellants consist of a single material, and aretermed monopropellants. Those propellants involving two materials aretermed bipropellants and normally consist of an oxidizer and a fuel.Hydrogen peroxide and nitromethane are each well known monopropellants.Well known bipropellants include hydrogen peroxide or liquid oxygen asthe oxidant with a fuel component such as ethyl alcohol-water, ammonia,hydrazine, or hydrogen; and nitric acid as the oxidizer with aniline ora furfuryl alcohol as the hypergolic fuel component. Other materialswhich can be used in bipropellants include the heterocyclicnitrogen-containing compounds such as pyrrole, N-alkyl pyrrole, andalkyl derivatives of said heterocyclic nitrogen-containing compounds.

When employing 90 to 100 percent or more nitric acid, i.e., white fumingnitric acid, as the oxidizer in a rocket propellant, it is oftennecessary, dependent on the specific fuel component, to make ignitionmore prompt by dissolving from 6 to 14 percent by weight of nitrogendioxide in the white fuming nitric acid, forming thereby red fumingnitric acid. A fuel component of one type of bipropellant materialdescribed herein, is spontaneously ignited upon contacting the oxidizer,and for that reason, is referred to herein as being a hypergolic fuel. Aratio of oxidizer to hypergolic'fuel, based on stoichiometric amounts,can be utilized within the limits of 0.5 :1 to 1.5 :1, if desired, theefliciency of the combustion being less at ratios below 1:1 and the useof the oxidizer being less economical at ratios above 1:1. However,tactical consideration may necessitate the use of higher ranges, even ashigh as 6:1.

Other types of reaction motors in which the fuels of the invention canbe utilized are the jet engines, i.e., ram jets, turbo-jets and pulsejets. The Working cycle of the ram jet and the turbo-jet is essentiallythe same. One distinct difference in operation, however, is apparent inthe compression step. Air is jammed into the combustion zone of theturbo-jet by a gas turbine. Compression in a ram jet engine is providedby the ramming effect of the oncoming air. Compression in the pulse jetengine is obtained by the ramming effect of the oncoming air and by theintermittent explosion of fuel which causes the closure of valvesupstream of the combustion zone to prevent the escape of gases throughthe upstream end of the engine.

Fuel which is injected into the combustion zone of the above-designatedjet engines may originally be ignited therein by a spark producingdevice, such as a conventional spark plug mounted in the wall of thecombustion chamber. Additional fuel is thereafter ignited by the flameof burning fuel or by the heat from hot combustion gases remaining inthe combustion zone or hot combustion chamber wall. The air and exhaustgases within the combustion zone are heated by the heat of combustionand are exhausted from the combustion zone through a rearwardlyextending exhaust conduit at an exit velocity higher than the flyingspeed of the engine. The thrust produced thereby equals the gas massflowing through the exhaust duct times its increase in speed, accordingto the law of momentum.

Various organic compounds, and especially certain non-hydrocarbons, areunstable in storage or in use, while being transferred, or duringtreatment, and form undesirable gums, undergo discoloration, becomerancid or otherwise deteriorate due to oxidation, polymerization, orother undesired reactions. Included among the organic non-hydrocarboncompounds which undergo such deterioration are the heterocyclicnitrogen-containing compounds containing one nitrogen atom and fourcarbon atoms in the ring. Various inhibitors have been employed in thepast to treat organic compounds in order to secure satisfactorystability. Although a large number of inhibitors have either beenproposed or used, there is a constant search for new and improvedinhibitors.

One important use of said heterocyclic nitrogen-containing compounds isas a reaction motor fuel. The problem of protecting such materials fromdeterioration during separation, manufacture, blending, storage, and useis important; and in many instances is essential for successfulutilization of these compounds. In recent years the degradation of fuelsfor use in reaction motors has become prominent. The presence of gummymaterials in the fuel interferes with the normal operation of the fuelsystem and injectors in reaction motors, thus lowering the efiiciency ofthe motor. Heterocyclic nitrogencontaining compounds having one nitrogenatom and four carbon atoms in the ring utilized for purposes other thanreaction motor fuels likewise require protection from deteriorationduring storage or use.

The following objects of this invention will be attained by at least oneof the aspects of the invention.

An object of this invention is to provide new rocket propellants.Another object of the invention is to provide an improved hypergolicfuel. Another object of the invention is to provide a method forimparting immediate thrust to a rocket. Another object of the inventionis to provide a rocket propellant having a freezing point suitable tomake such propellant useful at low temperatures. Another object of thisinvention is to provide a method for stabilizing heterocyclicnitrogen-containing compounds having one nitrogen atom and four carbonatoms in the ring. Another object of this invention is to preventformation of gum and undesirable color in said heterocyclicnitrogen-containing compounds during shipment or storage. Another objectof this invention is to provide stabilizing agents for said heterocyclicnitrogen-containing compounds. Other aspects, objects and advantages ofthe invention will be apparent to those skilled in the art upon study ofthis disclosure and the drawing.

According to the invention, there is provided a fuel compositionconsisting essentially of a heterocyclic nitrogen-containing compoundcontaining; one nitrogen atom and four carbon atoms in the ring and from0.1 to 54.6 percent by weight of a compound having the structuralformula wherein, each R is selected from the group consisting ofhydrogen, alkyl, and aryl hydrocarbon radicals, and n is an integer fromto 6.

Further according to the invention, there is provided a method ofstabilizing a heterocyclic nitrogen-containing compound containing onenitrogen atom and four carbon atoms in the ring which comprises admixingtherewith a stabilizing amount of a compound having the above structuralformula.

In the above formula, the various Rs can be the same or different. It ispreferred that n be an integer in the range of O to 6, more preferablyin the range of 0 to 4, because such compounds are normally liquid;however, 11 can be larger and the compound still be eifective. We havefound that when R is hydrogen the stabilizing action of the compound ismore effective than when R is a hydrocarbon radical; and further, thatthe smaller hydrocarbon radicals are preferred to the larger hydrocarbonradicals for the same reason. Therefore R preferably contains no morethan '6 carbon atoms. It is preferred that at least one R be selectedfrom the group consisting of hydrogen, methyl, ethyl, n-propyl, andisopropyl hydrocarbon groups, and the greater the number of such groupsthe more effective will be the stabilizing action of the compound.

Examples of compounds which can be used in the practice of the inventioninclude, among others, hydrazine, N,N,N,N-tetramethylhydrazine,N,N-diphenylhydrazine, ethylhydrazine, ethyl-phenylhydrazine, methylhydrazine, isopropylhydrazine, N,N-diphenyl-N,N-dimethylhydrazine,N,N,N,N-tetrapropylhydrazine, N,N-dihexyl- N,N-diethyl hydrazine, andthe like; methylene diamine, ethane-1,2-diamine, propane1,3-diamine,hexane-1,3-diamine, N,N-dimethyl ethane-1,2-diamine, N,N,N',N'-tetramethyl propane-1,3-diamine, N,N-dimethyl-N,N'-dihexylpentane-1,5-diamine, N,N,N-trihexyl hexane-1,6- diamine, N,N'-diphenylbutane-1,4-diarnine, and the like. Other compounds which are effectiveas stabilizing agents include N,N,N',N'-tetrapentyl octane-1,8-diarnine,N,N, N,N'-tetrahexyl octane-1,8-diamine, N,N,-dioctylheptane-1,7-diamine, tetraheptyl hydrazine and the like. Hydrazine isthe preferred stabilizing agent of the invention.

The heterocyclic nitrogen-containing compounds which can be stabilizedin the practice of the invention are the unsaturated heterocycliccompounds containing four carbon atoms and one nitrogen atom, and thealkyl derivatives of these heterocyclic compounds. Examples of thesepreferred compounds include, among others, pyrrole; N-alkyl-pyrrolessuch as N-methyl pyrrole, N-ethyl pyrrole, N-propyl pyrrole, N-butylpyrrole, N-amyl pyr role, and the like; alkyl derivatives of pyrrolesuch as 2- methylpyrrole, 2,5-dimethylpyrrole, 2-methyl-3-ethylpyrrole,2,4-diethylpyrrole, and the like.

The stabilizing agents of this invention are not necessarily equivalentin their effects and it should be understood that they cannotnecessarily be used to replace one another with equal effect, either ona weight or chemically equivalent basis. The quantity of stabilizingagent employed will vary, but in general will range from about 0.1 to 5weight percent, preferably from 0.1 to 3 weight percent. Amounts ofstabilizing agent in excess of 3 weight percent are generally notdesirable from the stand point of economics. This is demonstrated by thespecific examples given hereinafter. The exact quantity required is afunction of the stabilizing agent used and of the heterocyclicnitrogen-containing compound as well as the desired stability of theorganic compound treated.

Many of the above-mentioned heterocyclic nitrogencontaining compoundsare useful as solvent materials, as reagents in chemical synthesis, oras reactants or other purposes in the chemical industry. In addition,pyrrole and N-methylpyrrole, for example, are all desirable reactionmotor fuels, and when stabilized against discoloration and gum formationwith hydrazine, for example, are particularly suitable as a fuel for areaction motor such as a rocket, ram-jet, etc.; especially since theperformance of the fuel, which includes such factors as ignition delay,specific thrust, and burning characteristics, will also be improved. Thepresent invention provides a simple and economical method for thestabilization of said heterocyclic nitrogen-containing compounds so thatthe materials can be stored for relatively long periods or shipped longdistances without gum formation or discoloration in appreciable amounts.

As pointed out hereinabove, hydrazine has been known as a fuel componentin a bipropellant system. The use of this material at high altitude hasbeen accompanied by attendant disadvantages, however, for hydrazine hasa freezing point of 1.5 C. (+29" F.). Obviously, unless that freezingpoint is lowered, use of that fuel in a rocket would be impractical.

In one broad aspect our invention comprises a fuel utilizing up to 56percent by volume (57.6 weight percent) of hydrazine, which does nothave a freezing point sufficiently low to make its use generallypractical in jet engines, in at least 44 percent by volume (42.4 weightpercent) of pyrrole, which has too high a freezing point to make its usegenerally practical in an unmodified form. A minor amount, generallybetween 4 and 16 percent by volume (4.2 to 16.8 weight percent),preferably 8 to 13 percent by volume (8.4 to 13.7 weight per cent), ofanhydrous hydrazine in pyrrole provides the low freezing point necessaryto make the use of the fuel practical over a much wider range ofoperating condi tions. Hydrazine in an amount of about 11.5 percent byvolume (12.1 weight percent) results in lowering the freezing point ofpyrrole to its lowest point. Slightly lower freezing points can beattained by incorporating water in an amount up to 4 percent by volumebased on the hydrazine. Between 36 and 5 3 percent by volume (37.5 to54.6 weight percent), preferably 44 to 51 percent by volume (45.6 to52.7 weight percent), of hydrazine in pyrrole also results in a materiallowering of the freezing point of the resulting mixture.

Better understanding of this aspect of the invention will be apparentupon study of the drawing which is a graphic representation of theresult of lowering the freezing point ofthe total fuel to practicallimits by the addition of minor amounts of anhydrous hydrazine to amajor amount of pyrrole. 1

Thus, in accordance with our invention, we have provided a novelbipropellant fuel which comprises pyrrole and hydrazine. The pyrrole hasgoodrocket fuel characteristicswith the exception of 'a freezing pointwhich is too high for general practical use. The freezing point of purepyrrol'e is 24 C. (-11 F.). However, for general practical use as arocket fuel, the freezing point is preferably at least as low as '35 C.(31 F.).

We have discovered that when a minor amount of hydrazine, for example 4to 16 percent by volume (4.2 to 16.8 weight percent), either anhydrousor containing up to 5 percent by volume of water, is added to between 84and 96 percent by volume (83.2 to 95.8 weight percent) of pyrrole as setforth herein, the freezing point of the composite fuel is lowered tosuch an extent that it is suitable for practical use as a rocketpropellant. The amount of pyrrole is preferably in the range of 87 to'92 percent by volume (86.3 to 91.6 weight percent) of the fuel. We havediscovered that a eutectic is formed when a minor amount of hydrazine isadded to pyrrole. Although the freezing point of pure pyrrole is 24 C.(-11 F.) and the freezing point of hydrazine is 1.5 C. (+29 F.), thefreezing point of the eutectic is considerably lower than the freezingpoint of either of the component materials when those componentmaterials are combined within a certain critical range. An additionaladvantage of the use of hydrazine as the minor portion of the fuel isthat the performance of the eutectic of hydrazine and pyrrole, whichincludes such factors as ignition delay, specific thrust and burningcharacteristics, is enhanced.

We have further found that a second eutectic is formed and that bycombining from 36 to 5 3 percent by volume (37.5 to 54.6 weightpercent), preferably 44 to 5-1 percent by volume (45.6 to 52.7 weightpercent), of hydrazine (anhydrous or containing up to 5 percent byvolume of water) in from 47 to 64 percent by volume (45.4 to 62.4 weightpercent) of pyrrole, a second lowering of the freezing point isobtained. Reference to the drawing will disclose that the addition ofany amount up to 57 percent by volume (59.2 Weight percent) results inat least some lowering of the freezing point of the pyrrole. In makingthe conversions herein of volume percent to weight percent 0.948 wasemployed as the density of pyrrole and 1.011 was employed as the densityof hydrazine.

salts such as the chlorides and naphthenat es' of iron, zinc, cobalt andsimilar heavy materials.

The advantages of this invention are illustrated in the followingexamples. The reactants and their proportions are presented as beingtypical and are not to be construed as unduly limiting of the invention.

EXAMPLE I EXAMPLE II A first series of test samples of pyrrolecontaining various amounts ranging from 0.0 to 5.0 weight percent ofhydrazine admixed therewith as a stabilizing agent was prepared.Ignition delay, refractive index, color, and steam jet gum tests wererun on a portion of each sample. Said gum tests were run in accordancewith ASTM method D381-54T. The remainder of each sample was placed in aclear one-half pint glass bottle. Said bottles were filled approximatelythree-fourths full. Said bottles, open to the atmosphere, were thenstored under essentially dark storage conditions by placing the bottlesin an oven maintained at approximately 140 F. for a period of days. Atthe end of the 60 days storage period, the above named tests were againrun on the stored samples.

A second series of test samples of N-methylpyrrole containing variousamounts ranging from 0.0 to 5 .0 weight percent of hydrazine admixedtherewith as a stabilizing agent was prepared and tested as describedabove.

The results of the tests on both series of samples are given in thetable below. It is evident from a comparison of the data in said tablethat hydrazine is an effective stabilizing agent.

Table GUM AND COLOR STORAGE STABILITY, 140 F., 60 DAYS Start Test EndTest Fuel Weight Steam jet Steam jet percent Ignition R.I. NPA gum, mg/Ignition R.I. NPA gum, mg Hydrazine Delay Color 100 1 Delay Color 100ml.

added Pyrrole control 0. 0 42.1 4. 4 onelszlog o. 5 165.1 2.8 7313 1. 039. 8 3. 0 61. 8 3. 0 36. 0 1. 8 28. 6 5. 0 46. 3 1. 2 34. 3 Pyrrolecontrol-l- 1.0 111. 8 N -Methy1 Pyrrole control 0. 0 21. 0 N-MethylPyr'role-l- 0.5 15. 9 N -Methyl Pyrrole+ 1.0 15. 1 N-Methyl Pyrrole+ 3.09. 6 N-Methyl Pyrrole control 1. 0 37. 2

Other oxidizers are suitable as oxidants for hypergolic EXAMPLE IIIfuels, in addition to white or red fuming nitric acid, and can be usedin the practice of our invention. Suitable oxidants include materialssuch as hydrogen peroxide, ozone, nitrogen tetraoxide, liquid oxygen andmixed mineral acids, especially anhydrous mixtures of nitric andsulfuric acids, such as 80-90 percent by volume white or red fumingnitric acids and 10-20 percent by volume anhydrous or fuming sulfuricacid. It is Within the scope of this invention to employ, preferablydissolved in the oxidizer, ignition catalysts or oxidation cata- Steamjet gum tests (ASTM D381-54T) were run on another control sample ofN-methylpyrrole and a sample of N-methylpyrrole containing 5 weightpercent of N,N,N',N'-tetramethylpropane-1,3-diamine, which samples hadbeen stored under the conditions described in Example II. After storageas described, the gum content of the N-methylpyrrole containing nostabilizer was 321.4 milligrams per 100 milliliters, whereas the gumcontent for the sample of N-methylpyrrole containing said stalysts.These oxidation catalysts include certain metal bi izel Was only 3 -3milligrams p r 0 m l i r bu'stion of bipropell'ant components in? acombustion.

chamber of a reaction motor, the steps comprising separately andsimultaneously injecting a stream of an oxidant component and a streamof a fuel component into a combustion chamber of said motor inproportions, based on stoichiometric amounts,.within the range of 0.5 :1to 1.5 1, said fuel component consisting essentially of a heterocyclicnitrogen containing compound selected from the group consisting ofpyrrole and N-methyl pyrrole, and a second compound selected from thegroup consisting. of hydrazine and N,N,N',N-tetramethylpropane-1,3-diamine; wherein: when said hydrazine is present in saidfuel component it is present in an amount within the ranges of about 0.5to 16 percent inclusive and about .36 to 53 percent inclusive; and whensaid diamine is present in said fuel component it is present in anamount within the range of about 0.1 to about percent.

2. The method of'cl'aim 1 wherein said fuel component consistsessentially of pyrrole and about 4 to about 16 percent by volumehydrazine.

3. The method of claim 1 wherein said fuel component consistsessentially of pyrrole and between 36 and 53 percent by volume ofhydrazine.

4. The method of claim 1 wherein said nitrogen containing compound isN-methyl pyrrole and said second compound is N,N,N,N-tetramethylpropane-1,3-diamine.

5. In the method for developing thrust by the combustion of bipropellantcomponents in a combustion chamber of a reaction motor, the stepscomprising separately and simultaneously injecting a stream of anoxidant component and a stream of a fuel component into a combustionchamber of said motor in proportions, based on stoichiometric amounts,within the range of 0.5: 1 to 1.5 1, said fuel component consistingessentially of pyrrole and from about 0.1 to about 5 percent by weightof N,N,N,N- tetramethyl propane-1,3-diamine.

6. The method of claim 5 wherein said diamine is present in an amountwithin the range of about 0.1 to about 3 percent by weight.

7. In the method for developing thrust by the combustion of bipropellantcomponents in a combustion chamber of a reaction motor, the stepscomprising separately and simultaneously injecting a stream of anoxidant component and a stream of a fuel component into a combustionchamber of said motor in proportions, based on stoichiometric amounts,within the range of 0.5 :1 to 1.5 1, said fuel component consistingessentially of about 11.5 percent by volume of hydrazine and about 88.5percent by volume of pyrrole.

8. In the method for developing thrust by the combustion of bipropellantcomponents in a combustion chamber of a reaction motor, the stepscomprising separately and simultaneously injecting a stream of anoxidant component and a stream of a fuel component into a combustionchamber of said motor in proportions, based on stoichiometric amounts,within the range of 0.5 :-1 to 1.5 :1,

said. fuel component consisting essentially of about 49" percent byvolume of hydrazine and about 51 percent by volume of pyrrole.

9. A fuel composition consisting essentially of a heterocyclic nitrogencontaining compound selected from the group consisting of pyrrole andN-methyl pyrrole, and a second compound selected from the groupconsisting of hydrazine and N,N,N',N-tetramethyl propane-1,3-diamine;wherein: when said hydrazine is present in said composition it ispresent in an amount within the ranges of about 0.5 to about 16 percentinclusive andabout 36 to about 53 percent inclusive; and when saiddiamine is present in said composition it is present in an amount withinthe range of about 0.1 to about 5 percent.

10. A fuel composition according to claim 9 wherein said nitrogencontaining compound is N-methyl pyrrole and said second compound isN,N,N,N-tetramethyl propane-1,3-diamine.

11. A fuel composition consisting essentially of pyrrole and from about0.1 to about '5 percent by weight of N,N,N',N-tetramethylpropane-1,3-diamine.

12. A fuel composition consisting essentially of pyrrole and 4 to 16percent by volume hydrazine.

13. A fuel composition consisting essentially of pyrrole and 8 to 13percent by volume hydrazine.

14. The fuel of claim 12 wherein said hydrazine is anhydrous.

15. The fuel of claim 12 wherein said hydrazine contains up to 5 percentwater.

16. A fuel composition consisting essentially of pyrrole and between 36and 53 percent by volume of hydrazine.

17. A fuel composition consisting essentially of pyrrole and between 44and 51 percent by volume of hydrazine.

18. A fuel composition consisting essentially of about 11.5 percent byvolume of hydrazine and about 88.5 percent by volume of pyrrole.

19. A fuel composition consisting essentially of about 49 percent byvolume of hydrazine and about 51 percent by volume of pyrrole.

References Cited in the file of this patent UNITED STATES PATENTS Klein:SAE Journal, December 1947, pages 22-28 incl. (Copy in ScientificLibrary.)

1. IN THE METHOD FOR DEVELOPING THRUST BY THE COMBUSTION OF BIPROPELLANTCOMPONENTS IN A COMBUSTION CHAMBER OF A REACTION MOTOR, THE STEPSCOMPRISING SEPARATELY AND SIMULTANEOUSLY INJECTING A STREAM OF ANOXIDANT COMPONENT AND A STREAM OF A FUEL COMPONENT INTO A COMBUSTIONCHAMBER OF SAID MOTOR IN PROPORTIONS, BASED ON STOICHIOMETRIC AMOUNTS,WITHIN THE RANGE OF 0.5:1 TO 1.5:1, SAID FUEL COMPONENT CONSISTINGESSENTIALLY OF A HETEROCYCLIC NITROGEN CONTAINING COMPOUND SELECTED FROMTHE GROUP CONSISTING OF PYRROLE AND N-METHYL PYRROLE, AND A SECONDCOMPOUND SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE ANDN,N,N'',N''-TETRAMETHYL PROPANE-1,3-DIAMINE, WHEREIN: WHEN SAIDHYDRAZINE IS PRESENT IN SAID FUEL COMPONENT IT IS PRESENT IN AN AMOUNTWITHIN THE RANGES OF ABOUT 0.5 TO 16 PERCENT INCLUSIVE AND ABOUT 36 TO53 PERCENT INCLUSIVE, AND WHEN SAID DIAMINE IS PRESENT IN SAID FUELCOMPONENT IT IS PRESENT IN AN AMOUNT WITHIN THE RANGE OF ABOUT 0.1 TOABOUT 5 PERCENT.